1. Technical Field
The field of the present invention relates to improvements in crimp press machines for crimping ferrules forming an end connection for a flexible hose.
2. Description of Related Art
Conventional radial crimp presses have a die set made up of a plurality of dies surrounding a work or crimping zone, each of the dies are caused to simultaneously move inwardly against an outer surface of a metal ferrule surrounding a flexible hose placed in the work zone, by an axially moving piston member acting under an applied hydraulic pressure, the objective being to plastically deform the ferrule radially inwardly onto the flexible hose such that the ferrule and the hose are permanently connected together. The number of dies in a die set can be any number but it is relatively common to provide eight such dies in a die set, uniformly positioned around the work zone. Any crimp press will be required to crimp a range of different hoses and ferrules, each having a particular desired finished end crimp diameter. In order to crimp to various diameters, the crimp press will be supplied with die sets of various inner diameters that can be selected and installed in the press. The change-over of desired die sets can, however, add time to a crimping process. The objective generally is to crimp a particular ferrule to a desired specific reduced diameter on a desired hose. This is achieved by selecting a die set one size smaller than the required diameter and installing this die set in the crimp press, entering the required diameter in the crimp press controller and entering a “required offset valve” into the crimp press controller, and carrying out the crimping process. The crimp press will halt at a certain position such that the inner diameter of the installed die set will crimp the ferrule to the required “reduced” diameter. The formula being, “Die Set Closure Diameter”+“Offset Value”=“Required Crimp Diameter.
The range of hoses and hose couplings are increasing. Hose assemblies are now required to operate more reliably and for many more cycles of use. Pressure ratings are generally also increasing. Further, innovative hose structures are being developed which must be able to have an end fitting (ferrule) crimped thereto. In the past, it was possible to have one die set per hose/hose coupling set, however crimp presses are now required to crimp to any diameter within a given range. One die set must be able to crimp any diameter within its “closure diameter” and max offset value.
The objective in a crimping process is to achieve the most round (cylindrical) crimped ferrule possible following a crimping process. Retention of the ferrule on the hose is enhanced by the use of multiple axially spaced annular ribs or teeth directed inwardly from an inner surface of the ferrule. The quality of retention of the ferrule on the hose and the operational life of the hose is affected by the roundness of the ferrule and therefore the aforesaid teeth following a crimping process. In practice, for a number of reasons, the crimping process is only able to achieve an approximation to the desired cylindrical shaping following a crimping process. Because the die sets having a specific die face curvature relating to their closure diameter, and they are required to crimp any diameter within a range, a compromise on “roundness” is accepted in practice. If the crimp press were supplied with many more die sets, then the operational range of each die set could be reduced and the end roundness would be less of a compromise. This, however, is generally not acceptable because of the increased cost of the crimp press and the increased process time as a result of the removal and installation of die sets into the crimp press. Thus there is a balance to be achieved involving the least number of die sets for achieving a desired level of performance.
An uncrimped ferrule will always be of larger diameter than the final crimp diameter of the ferrule and of the diameter of the “die contact surface” with the result being that as the die initially contacts the ferrule as the die starts to move radially inwardly, only the axial outer edges of the “die contact surface” engage with the ferrule. With further radial inward motion of the die elements, the ferrule is compressed in between the die elements but there is no compression underneath the die elements, i.e. between the axial outer edges of each die element. As a result, metal of the ferrule tends to bulge outwardly and inwardly in the zones between the die elements as the crimping process continues. Shaping of the inner annular ribs or teeth of the ferrule is also compromised producing an axially viewed shape tending to the polygonal rather than circular. When the crimping press utilizes eight die elements, the internal axially viewed shape tends to an octagonal shape. As a result, performance of the connection between the ferrule and the hose is compromised. In addition, because a crimping process occurs as a metal cold working process, the strength of the ferrule may be enhanced by the cold working process but this is non-uniform providing peripheral zones of enhanced strength interspaced by zones where the strength has not been enhanced. Further because the process described above provides a tangential compressive force component as well as a radial compressive force component at the contact edges of the die elements with the ferrule, a higher total compressive force is required to drive the die elements radially inwardly. Hence a more powerful (and therefore costly) crimp press is required.
The objective of the present invention is to provide a crimp press and a process of crimping that will seek to achieve a rounder inner ferrule configuration to improve performance of retention of a ferrule on a hose. A further preferred objective is to provide a crimp press and a process of crimping that will provide a more uniform peripheral strength of the ferrule after crimping.